For preventing re-adhesion of a label, there have been plural proposals of a tamper-proof label that is broken by itself on peeling the label to leave a part thereof on an adherend.
For example, PTL 1 describes a brittle label containing a base material, a breakable layer, and an adhesive layer having a concavo-convex shape. On peeling the label from the adherend, the breakable layer is broken in such a manner that at least a portion of the breakable layer that correspond to the convex portion of the adhesive layer remains on the adherend. Accordingly, the fact that the label has been peeled can be recognized by the naked eye with the breakable layer remaining. However, for easily recognizing the peeling of the label by the naked eye, the breakable layer necessarily contains a layer formed of a material capable of being visually recognized easily, such as a colored layer or a metallic luster layer, which may cause a problem of increased process steps for production thereof, thereby raising the cost. Furthermore, the adhesive layer is necessarily broken simultaneously with the breaking of the breakable layer, which may cause a problem that the stress necessary for peeling and the shape of the portion remaining on the adherend may not be stable.
As a label that prevents re-adhesion of the peeled label, there have been plural proposals of such a label that on peeling the label from an adherend, the base material of the label is deformed to a shape that is unable to restore the original shape.
For example, PTL 2 proposes a label containing an adhesive layer that is provided on a plastic film (base material) having a residual strain amount in the longitudinal direction of at least 10%. On peeling the label from an adherend, the plastic film is stretched and undergoes plastic deformation due to the tensile force required for peeling, and thereby the label is unable to be re-adhered on the original location. However, the label does not have such a structure that a part of the label remains on the adherend, and thus the fact that the label has been peeled may not be easily recognized by the naked eye.
PTL 3 proposes a sealing label containing a label that is obtained from a uniaxially stretched film of a resin composition containing from 30 to 75% by weight of a polyolefin and from 70 to 25% by weight of a filler, and an adhesive that is coated on the back surface of the label. On peeling the sealing label from an adherend, the label is easily broken, which is a favorable function as a sealing label, but there is a problem that the broken surface thereof has a linear shape, and thus is difficult to be recognized in the case where the label is re-adhered with the broken surfaces thereof butted each other.